Process of making monoammonium phosphate



Patented Ma rz, 1927.

UNITED STATES PATENT OFFICE.

ELDOIN' L. LARISON, ran nnnrcx r. rarcx, AND RAYMOND .1. cano, orANACONDA, MONTANA, ABSIGNOBS 'ro ANACO/NDA corrnn MINING coinaNY, orANACONDA,

uoNrANa.

PROCESS 01 mt} HONOAHIEORIUI PHOSPHATE R Drawing.

The gases produced by the destructive distillation of coal in themanufacture of coke contain a small amount of ammonia which is ordinarilrecovered as ammonium sulfate 6 l iy scrub ing the gases with sulfuricacid. he ammonium sulfate made in this way is used chiefl as afertilizer and is valued by its availab e' nitrogen content, each onepercent of ammonia in the product being rated 10 as one unit of plantfood. The product ordinarily contains 25% ammonia or 25 units of plantfood, the sulfur and ox gen content being of negli ible value as aertilizer.

An object o the present invention is the 16 recovery of the ammoniacontent of coke oven gases and the like in a form having a higher plantfood value than the ammonium sulfate product referred to. Logically thismay be accomplished by combining the am- 20 monia with u an acidcomponent such as nitrate or phosphate which itself has a plant foodvalue or with which ammonia forms a compound of which the ammoniaconstitutes a greater proportion than in ammonium sulfate.

In ammonium phosphates, for instance, both the NH content and the P,O,content are rated as plant foods, but the diand tri-ammonium phosphatesare unstable compounds which are not suitable for fertilizer purposesand the production of mono-ammonium phosphate involves certain technicaldifliculties. For instance, if a gas consisting of or containing ammoniasuch as coke oven gases is passed into a crude solu tion of phosphoricacid (made by acidulating phosphate rock with sulfuric acid andseparating the calcium sulfate and other insoluble matter) of suchconcentration as to produce solutions which are saturated with respectto mono-ammonium phosphate a sludge results which is so thick that theabsorptioh of ammonia is difiicult. This is due in part to the fact thatthe mono-ammonium phosphate is very soluble in water making its supersaturated solution very thick and viscous and in part to the fact thatiron and aluminum compounds present Application filed Kay 3, 1926.Serial No. 106,546.

in the crude phosphoric acid are recipitated by the ammonia asgelatinous ydroxides. Besides it is difiicult to regulate theroportlonsof ammonia and phosphoric acid in the reactlon mixture so thatonly the .stable mono-ammonium salt is formed.

A further object of the invention therefore is to devise a process forthe roduction of mono-ammonium phosphate w ereby the diflicultiesreferred to are overcome. The process of the invention is designedprimarily for the production of more or less crude mono-ammoniumphosphate suitable for use as a fertilizer from inexpensive startingmaterials such as coke oven or similar ammonia containing gases andcrude phosphoric acid such as that produced by the acidu-lation ofphosphate rock, but as will be apparent the principles of the inventionare applicable in the use of other starting materials as, for instance,the ammonia containing gases produced by the synthesis of hydrogen andnitrogen and "by the decomposition of cyanamide with steam.

We have found that mono-ammonium phosphate may be preparedsatisfactorily bv treating a solution of phosphoric acid, suc as thecrude solution produced by the acidulation of phosphate rock, withammonia or ammonia containing gases such as coke oven gases by combiningthe ammonia and the phosphoric acid in such proportions, about 1 part bI weight of NH to 2.8 parts by weight o P O that about half of the phosphoric acid is combined as mono-ammonium phosphate and the remainder iscombined as the (Ii-ammonium phosphate and treating the resultingunstable salt in a separate operation with phosphoric acid in quantitysuificientto convert its di-ammonium phosphate content to themono-ammonium phosphate.

The first step of the process is conveniently carried out in thescrubbers or saturators customarily employed for the production ofammonium sulfate from coke oven gases although it will be understoodthat any suitable apparatus for gas and liquid contact may be employed.

e following description of a specific procedure illustrates theinvention: The saturator is charged with a suitable volume .of crudephosphoric acid solution of a concentration giving a hydrometic test ofabout 36 B. preferably warmed to about continuous supply of crudephosphoric acid to the saturator are started and maintained at suchrates that the ratio of NH and P 0 and the volume of liquid'in thesa'turator are maintained, the operation being continuous. Forcontrolling the operation of the saturator so as to maintain the NH P 0ratio at about 1:28 sam les of the saturator liquid are withdrawn rom'time to time, filtered,

and treated with a standard acid such as sulfuric acid using methylorange as the indicator.- Methyl orange is yellow when the ratio ofammonia to phosphoric acid is greater than that in mono-ammonium phosphate and turns red when this excess of ammonia is consumed by thetitrating acid. The supply of crude phos horic acid and the removal ofpulp may, 0 course, be varied as required to maintain the statedconditions.

-It has been found theta saturator liquid of the composition referred toabsorbs ammonia readlly and efficiently and the composition of theliquid is readily'controlled in continuous operation. The ratio of NH,to

P 0 in the scrubber li uid may of course The ammo-' niated pulpwithdrawn from the saturator vary with reasonable llmits.

is mixed with phosphoric acid in quantity suflicient to convert theunstable di-ammonium phosphate in it into the stable monoammoniumphosphate and the resulting mono-ammonium phosphate sludge is dried in arotary or other suitable drier to such a moisture content that it may beground and applied to soil by means of the usual fertilizer distributingmachinery.

Mono-ammonium phosphate when pure contains 14.7 8% of NH and 61.74% of P0 or 76.52 units of plant food and the crude product produced asdescribed approaches this figure. he crude mono-ammonium phosphate mayof course be refined and purified, for instance, by diluting theneutralized pulp with water in quantity sufiicient to dissolve themono-ammonium phosphate, filtering the solution and crystallizcontactinging out the mono-ammonium phosphate by concentration.

We claim:

1. Process of making ammo-ammonium phosphate which comprises combiningammonia and phosphoric acid in the ratio of approximately 1 part byweight of NH to 2.8 parts by weight of P 0 and treating the resultinmixture of monoand di-ammonium p osphate with phosphoric acid inquantity suflicient to convert the di-ammonium phosphate into themono-ammonium phosphate.

2. Process of making mono-ammonium phosphate which comprises scrubbin agas containin ammonia with a solutlon of phosphoric acid until the ratioof NH to P 0, in the scrubbing liquid is about 1 to 2.8 b weight.

3. Process of making mono-ammonium phosphate which comprises scrubbing agas containing ammonia with a li uid containing monoand di-ammonium posphate and maintaining the ratio of NH, to P 0, in the scrubbing hquidat about 1 to 2.8 by weight.

4. Process of making m'ono-ammomum phosphate which comprisescontinuously a stream of gas containing ammonia with a scrubbing liquidcontainin monoand (ii-ammonium phos hate and maintaining the ratio of NH, to ,0,, in the scrubbing liquid at about 1 to 2.8 b wei ht bycontinuously withdrawing scrub in ,iquiddand continuously supplyingphosp one am 5. Process of making mono-ammonium phosphate whichcomprises scrubbing a containin ammonia with a crude SOllltlOll of phosporic acid of about 36 B. contaimn 1ron and aluminum. compounds obtainabe by acidulating phosphate rock with sulfuric acid until the ratio ofNH, to P50, in the scrubbing liquid is about 1 to 2.8 by weight.

6. Process of makin K mono-ammonium phosphate which comprlses scrubbingcoke oven gases containing ammonia with a solution containing monoanddi-ammonium phosphate, maintaining the ratio of NH, to P 0 in thescrubbing liquid at about 1 to 2.8 by'weight'by the removal ofammoniated sludge from and the addition of phosphoric acid solution ofabout 36 B6. to the scrub bin liquid, and treating the withdrawn sludgewith phosphoric acid in quantity sufiicient to convert its di-ammoniumphospfiate content into mono-ammonium phosp ate.

7. Process of making a mono-ammonium phosphate product suitable for useas fertilizer which comprises scrubbin coke oven gases containinglammonia wit a liquid containing NH and P50 in about the ratio of 1 to2.8 by weight, maintaining the volme and composition of the scrubbingliquid by the withdrawal of ammoniated sludge mono-ammonium phosphate,and drying the 1'.

and the addition of crude phosphoric acid of resulting product.

about 36 B. containing iron and aluminum In testimony whereof, we aflixour signacornpounds obtainable by the acidulation of tures.

phosphate rock with sulfuric acid, treatin the withdrawn sludge withphosphoric aci ELDON L. LARISON. in quantity suflicient to convert thedi-am- FREDERICK F. FRICK. monium phosphate content thereof into o iRAYMOND J. CARO"

